Imaging devices, such as cameras, can be used to capture images of portions of the electromagnetic spectrum, such as the visible light spectrum, incident upon an image sensor. For ease of discussion, the term light is generically used to cover radiation across the entire electromagnetic spectrum. In a typical imaging device, light enters through an opening (aperture) at one end of the imaging device and is directed to an image sensor by one or more optical elements such as lenses. The image sensor includes pixels or sensor elements that generate signals upon receiving light via the optical element. Commonly used image sensors include charge-coupled device (CCDs) sensors and complementary metal-oxide semiconductor (CMOS) sensors.
Image sensors are devices capable of converting an optical image into a digital signal. Image sensors utilized in digital cameras are typically made up of an array of pixels; the number of pixels determines the megapixel rating of the image sensor. For example, an image sensor having a width×height of 2272×1704 pixels would have an actual pixel count of 3,871,488 pixels and would be considered a 4 megapixel image sensor. Each pixel in an image sensor is capable of capturing light and converting the captured light into electrical signals. In order to separate the colors of light and capture a color image, a Bayer filter is often placed over the image sensor, filtering the incoming light into its red, blue, and green (RGB) components that are then captured by the image sensor. The RGB signal captured by the image sensor using a Bayer filter can then be processed and a color image can be created.
In photography, depth of field is the distance between the nearest and farthest objects in a picture that appears acceptably sharp. Depending on the desire of the photographer, it can be desirable to have the entire image be sharp, in which case a large depth of field is desired. Conversely, a small depth of field will emphasize certain aspects of a picture (that will appear sharp) while de-emphasizing the other aspects of the picture (that will appear out of focus). When taking pictures, the size of the image sensor corresponds to the depth of field of the image captured by the image sensor, with smaller sensors having a larger depth of field. Alternately, a variable aperture in front of the lens adjusts to vary the depth of field captured—a smaller aperture enabling a larger depth of field and vice versa. Cellular telephones are often equipped with a small digital camera, often employing an image sensor around 4 mm. This gives cellular telephone cameras a large depth of field. For comparison, an image sensor in a DSLR camera typically measures between 18 mm and 36 mm, giving a DSLR a smaller depth of field than a cellular telephone camera. This is assuming that both the DSLR and the cellular telephone camera have maximal aperture settings for the captured photographs.